Southwest drought ending with onset of El Nino

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With the onset of an El Nino weather pattern and decline of La Nina, weather forecasters are saying that the coming winter will be cooler and wetter than normal. That situation should persist into March, says Steve Lyons, National Weather Service, San Angelo, Texas.

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The drought that has covered most of the Southwest for two years is coming to an end.

With the onset of an El Nino weather pattern and decline of La Nina, weather forecasters are saying that the coming winter will be cooler and wetter than normal. That situation should persist into March, says Steve Lyons, National Weather Service, San Angelo, Texas.

Lyons said little will change over the next 90 days. “We predict warm and dry conditions until about Christmas, and then it turns cooler and wetter.”

The last 90 days, to no one’s surprise, has featured below average rainfall and above average temperatures.

“We’ve been running much above normal temperatures,” he said, “much like last year, and that does not help with evaporation.”

Those evaporation losses expose a situation that has longer-term and possibly more severe ramifications than the soil drought that has covered the region for two years. A return to more normal—or slightly cooler and wetter conditions this winter—could break the drought. But a hydrologic drought could persist for years.

A hydrologic drought results when surface water—including reservoirs and streams— are depleted faster than they can be replenished because of prolonged drought. Lyons says a hydrologic drought exists when catchments are depleted to zero to 30 percent of full. When reservoirs get that low, “It takes a long time to fill them back up. One rain event will not be enough. We need widespread rainfall.”

Hydrologic drought is evident in much of West Texas. Near San Angelo, the O.C. Fisher and E.V. Spence reservoirs are at zero percent; Twin Buttes is at 5 percent. Near Abilene, Abilene Lake is at 11 percent; Hords Creek Lake is at 9 percent and Lake Stamford is at 35 percent.

“It may take several years to replenish these lakes,” Lyons said. “And that is if the drought doesn’t get worse.”

That also assumes wetter than average years. With a “wetter than normal,” prediction for the coming winter, a situation the region “has not seen for awhile,” reservoirs will not make appreciable progress to refill, Lyons said.